Chapter 13-Alkenes

Question 1

Are Alkenes saturated? What does saturated mean?

Answer 1

They are unsaturated. Saturated means it contains at least 1 carbon double bond

Question 2

What is an orbital?

Answer 2

A region around the nucleus which holds up to 2 electrons with opposite spins

Question 3

What is a pi bond and how is it formed?

Answer 3

A double bond. Formed by the sideways overlap of 2 p orbitals. Causes high electron density above and below sigma bond

Question 4

Why does E/Z isomerism exist in alkenes

Answer 4

Because the p bond locks the 2 bonded atoms in position and prevents rotation around the double bond

Question 5

What is the bond angle in alkenes?

Answer 5

Around the double bond, the bond angle is 120° and the shape is a trigonal planar. Everywhere else the shape is tetrahedral

Question 6

What is a stereoisomer?

Answer 6

Same structural formula but a different spatial arrangement of atoms

Question 7

What are the conditions required for E/Z isomerism?

Answer 7

A C=C bond

Different groups attached to each carbon in the double bond

Question 8

What is an E isomer and what is a Z isomer?

Answer 8

E isomers have the higher priority groups on different sides. Z isomers have higher priority groups on the same side

Question 9

What is cis/trans isomerism?

Answer 9

It is a special case of stereoisomerism where each C in the double bond must be attached to 1 hydrogen atom

Question 10

Cahn-Ingold-Prelog nomenclature-how is priority assigned?

Answer 10

Higher priority given to the atom with highest atomic number

Question 11

Why are alkenes more reactive than alkanes?

Answer 11

They have a pi bond

Question 12

Conditions required for hydrogenation of alkenes

Answer 12

423K temperature

Nickel catalyst

Question 13

What are the products of hydrogenation of alkenes?

Answer 13

Alkane
All double bonds are hydrogenated
Addition reaction, only one product

Question 14

What are the conditions required for halogenation of alkenes

Answer 14

Room temperature and pressure

Question 15

What are the products of halogenation of alkenes?

Answer 15

Haloalkane

Question 16

What is halogenation used for and how is this process carried out?

Answer 16

Used to determine whether a substance is an alkene or an alkane. When a few drops of bromine water are added, the alkene decolourises. If the same thing is done to an alkane, there will be no colour change

Question 17

What are the conditions required for adding hydrogen halides to alkenes

Answer 17

Gaseous hydrogen halides

Room temperature and pressure

Question 18

How is the reaction of alkenes and hydrogen halides carried out?

Answer 18

If the alkene is a liquid, the hydrogen halide is bubbled through it
If the alkene is a gas, the reaction occurs when the 2 gases mix
Gaseous hydrogen halide

Question 19

What are the products of reacting alkenes with hydrogen halides?

Answer 19

2 possible products in an unsymmetrical molecule, the halogen could be put on either side of double bond.
Becomes a haloalkane

Question 20

What are the products of hydration of alkenes?

Answer 20

Alcohol

2 possible products-functional group goes on either side of double bond

Question 21

What are the conditions required for hydration of alkenes?

Answer 21

Phosphoric acid catalyst

Question 22

What is an Electrophile

Answer 22

An electron pair acceptor

Usually a positive ion or something

Question 23

What is a nucleophile

Answer 23

Electron pair donor

Attracted to positive charges

Question 24

How does the H—Br bond break?

Answer 24

Heterolytic fission

Question 25

What is a carbocation

Answer 25

Molecule containing a positively charged carbon atom

Question 26

How is a dipole induced in Br2

Answer 26

Pi bond has a high electron density, which repels electrons in bromine, inducing a dipole

Question 27

What is Markownikoff’s rule?

Answer 27

When a hydrogen halide reacts with an unsymmetrical alkene, the hydrogen attaches itself to the carbon atom of the alkene with the greater number of hydrogen atoms and the fewer number of carbon atoms

Question 28

Primary Carbocation

Answer 28

Positive carbon on the end of a chain(attached to 1 carbon, 2 hydrogen)

Question 29

Secondary carbocation

Answer 29

Positive carbon in the middle of a chain(attached to 2 carbons and 1 hydrogen)

Question 30

Tertiary carbocation

Answer 30

Positive carbon attached to no hydrogens

Question 31

What is the stability trend with carbocations

Answer 31

Primary least stable, tertiary most stable
Because each alkyl group donates and pushes electrons towards the positive charge
The more alkyl groups the more +ve charge is spread out

Question 32

Recycling

Answer 32

• reduces environmental impact by conserving finite fossil fuels
• discarded polymers are sorted
• chopped into flakes
• washed, dried, melted
• cut into pellets, then used by manufacturers

Question 33

PVC recycling

Answer 33

• hazardous due to high chlorine content and additives
• dumping in landfill unsustainable
• when burnt, releases HCl and other pollutants
• use solvents to dissolve the polymer
• PVC then recovered from precipitation from the solvent

Question 34

Using waste polymers as fuel

Answer 34

• derived from petrol or natural gas so high stored energy value
• can be incinerated to produce heat, generating steam to power a turbine producing electricity

Question 35

Feedstock recycling

Answer 35

Chemical and thermal process which reclaim monomers, gases or oil from waste polymers.
Products resemble those produced from crude oil refineries
Can handle unsorted and unwashed polymers

Question 36

Bioplastics

Answer 36

Produced from plant starch cellulose, plant oils and proteins
Renewable alternative to oil based products

Question 37

Biodegradable polymers

Answer 37

Broken down by microorganisms into water
Made from starch or cellulose
Degrade and leave no visible or toxic residues

Question 38

Photodegradable polymers

Answer 38

Contain bonds that are weakened by absorbing light to start the degradation